1. Field of the Invention
The present invention relates to fluid seals, and in particular, to devices and systems for sealing fluids at very high pressures.
2. Description of the Related Art
Sealing fluids at extremely high pressures, i.e., pressures in excess of 15,000 psi, can be extremely difficult and complicated. FIG. 5 illustrates a high pressure seal according to the prior art. In the illustrated example, a plug 10 is engaged with a cylinder wall 12 having a circular mouth. An exterior surface 14 of the plug 10 is closely conformed to an interior surface 16 of the cylinder wall 12. A circular gap 18 is formed between the plug 10 and the cylinder wall 12. An annular recess 20 is formed in the external surface 14 of the plug 10 at a distal end 22 of the plug.
A metallic ring 24 with a triangular cross-section is positioned within the recess 20 with its right-most edge 26 abutting a complementary angled wall 28 of the recess. The metallic ring 24 is sized to slide with the plug 10 with respect to the internal surface 16 of the cylinder wall 12 when the system is not pressurized. This allows the plug 10 to be inserted and removed from the cylinder wall 12 to provide access to a cavity 30.
A polymeric backup ring 32 (sometimes referred to as a seal) is positioned to the left of the metallic ring 24, as viewed in FIG. 5. An angled, left-most edge 34 of the metallic ring 24 abuts a complementary tapered edge 36 on the polymeric backup ring 32.
An O-ring 38 is positioned on the side of the polymeric backup ring 32 opposite the metallic ring 24. The O-ring 38 is large enough to extend from the recess 20 to the internal surface 16 of the cylinder wall 12. The O-ring 38 seals the cavity 30.
When a fluid in the cavity 30 is pressurized, the O-ring 38 is urged against the polymeric backup ring 32 which, in turn, is urged against the metallic ring 24. The tapered edge 36 of the polymeric backup ring 32 presses against the angled, left-most edge 34 of the metallic ring 24, creating an upward force that urges the metallic ring against the internal surface 16 of the cylinder wall 12. In addition, as the metallic ring 24 is urged toward the right, as viewed in FIG. 5, the wall 28 of the recess 20 also urges the right-most edge 26 of the metallic ring upward against the internal surface 16 of the cylinder wall 12. In addition, the pressurized fluid operates on the left-most edge 34 of the metallic ring 24, adding to the force urging the metallic ring against the internal surface 16 of the cylinder wall 12.
As a result of the combined forces described above, the metallic ring 24 is urged against the internal surface 16 of the cylinder wall 12 with a very high force. As a result, the force the metallic ring 24 exerts on the internal surface 16 is so great that relative movement between the two galls and scratches one or both of the contacting surfaces.
When the fluid in the cavity 30 is pressurized to extremely high pressures (i.e., over 15,000 psi), or more so when the fluid is pressurized to even greater pressures (e.g., over 75,000 psi or over 100,000 psi), the cylinder wall 12 expands outward and the plug 10 compresses toward the right as viewed in FIG. 5. The expansion and movement of these parts results in relative movement between the metallic ring 24 and the internal surface 16 of the cylinder wall 12. Every time the pressure in the cavity 30 is cycled, the metallic ring 24 expands and contracts, further galling and scratching either the metallic ring and/or the cylinder wall 12. Eventually, scratches or other damage allows fluid to escape from the cavity 30, ultimately resulting in seal failure. In addition, it has been recorded that after a number of cycles, the metallic ring 24 can become lodged against the cylinder wall 12, requiring further repair and replacement of parts of the system.
Attempts have been made to coat the metallic ring 24 with materials that prevent or delay damage. It has been found, however, that such coatings are only temporary and, ultimately, the metallic ring 24 again fails, as described above.
The present invention is directed toward seals and seal systems for use with high pressure fluid containment systems. Embodiments of the invention allow a plug or other closure to be easily, manually engaged with and disengaged from a pressure vessel, while affecting a fluid seal at extreme elevated pressures. Embodiments of the invention will not scratch or gall the seal or the internal surface of the pressure vessel, and will not become lodged within the pressure vessel, as were commonly experienced with prior art seals.
One embodiment of the present invention incorporates a metallic ring having inner and outer surfaces. The inner surface is adapted to be received within a recess in a plug or other closure, and the outer surface is adapted to closely conform with an internal surface of a mouth on a pressure vessel. The maximum unstressed diameter of the metallic ring is equal to or slightly less than the diameter of the mouth to allow the closure to be manually inserted into and removed from the mouth when fluid in the pressure vessel is not pressurized. An edge on the metallic ring is adapted to sealingly conform to a complementary edge on the recess when the seal is subject to an elevated pressure. The metallic ring is made from a material having a modulus of elasticity that is sufficiently low such that, when the fluid is pressurized, the fluid pressure expands the metallic ring against the wall of the pressure vessel with a force sufficient to prevent extrusion of an O-ring. At the same time, however, the modulus of elasticity of the material of the metallic ring is small enough such that the force between the metallic ring and the wall is insufficient to generate a shear load great enough to gall the metallic ring when the metal ring moves with respect to the wall.
In another embodiment of the present invention, the seal incorporates a metallic ring having an inner surface, an outer surface, and an edge similar to those described above. In this embodiment, however, the metallic ring has a specific width that is selected to provide a desired pressure area. The width corresponds to the portion of the outer surface that contacts the wall of the pressure vessel. In the present invention, the width is large enough such that, when the fluid is pressurized, the metallic ring expands against the wall of the mouth with a force sufficient to prevent O-ring extrusion. At the same time, however, the width is small enough such that the force is insufficient to generate a shear load great enough to gall the metallic ring when the metallic ring moves with respect to the internal surface.
In another embodiment of the present invention, the metallic ring incorporates a first ring and a second ring. The first ring can be configured according to either of the above embodiments. The second ring is spaced apart from the first ring and is configured to retain at least one O-ring in the space between the first and second rings. In some alternate embodiments of this invention, the first and second rings are connected by an elongated neck of metallic material. The length and thickness of the neck are selected such that the mass of the second ring does not adversely affect the performance of the first ring.
The present invention is also directed toward pressure vessels incorporating the above-described seals.